THE  UNIVERSITY 

OF  ILLINOIS 

LIBRARY 

630.7 
II6b 


co 


A6RICULTURAL 
UBBARY 


UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  233 


SWEET  CLOVER   FOR  NITRATE 
PRODUCTION 

BY  ALBEET  LEMUEL  WHITING  AND 
THOMAS  E.  RICHMOND 


URBANA,  MAY,  1921 


CONTENTS  OF  BULLETIN  No.  233 

PAGE 

INTRODUCTION 255 

Characteristics  that  Make  Sweet  Clover  a  Valuable  Green-Manure  Crop . .  255 
Studies  by  Other  Investigators  on  Sweet  Clover  as  a  Green  Manure ....  256 

PLAN  OF  INVESTIGATION 258 

.    SWEET  CLOVER  FOR  NITRATE  PRODUCTION  ON  BROWN  SILT 

LOAM 259 

Results  Obtained  at  Urbana,  University  North  Farm,  1918 259 

Results  Obtained  at  Minonk  Field  in  1919 -. .  .261 

SWEET  CLOVER  FOR  NITRATE  PRODUCTION  ON  GRAY  SILT  LOAM 

ON  TIGHT  CLAY '...  .263 

Results  Obtained  at  Toledo  Field  in  1919 263 

Results  Obtained  at  Newton  Field  in  1919 264 

Results  Obtained  at  Oblong  Field  in  1919 264 

WEIGHTS  AND  NITROGEN  CONTENT  OF  SWEET  CLOVER . . . '. 266 

CONCLUSIONS  .  ..267 


SWEET  CLOVER  FOR  NITRATE 
PRODUCTION 

BY  ALBERT  LEMUEL  WHITING,  CHIEF  IN  SOIL  BIOLOGY,  AND 
THOMAS  E.  EICHMOND,  ASSOCIATE  IN  SOIL  BIOLOGY 

INTRODUCTION 

Sweet  clover  offers  the  most  promising  indications  that  the  problem 
of  supplying  a  cheap  source  of  nitrate  nitrogen  for  farm  crops  can 
be  solved.  With  the  exception  of  manure,  the  animal  sources  of 
nitrogen,  such  as  tankage,  dried  blood,  fish  meal,  guano,  and  others, 
are  limited  in  quantity,  and  their  price  is  such  that  to  use  any  of 
them  except  manure,  as  a  source  of  nitrogen  for  crop  growth,  is  out 
of  the  question.  The  chemicals,  Chili  saltpeter  or  sodium  nitrate, 
calcium  nitrate,  ammonium  nitrate,  ammonium  sulfate,  ammonium 
phosphate,  calcium  cyanamid,  and  others  are  likewise  too  expensive 
to  apply  to  soils  on  which  staple  crops  are  to  be  grown. 

The  need  for  special  studies  to  determine  the  value  of  sweet  clover 
(Melilotus  alba,  sometimes  called  bee  clover)  for  nitrate  production, 
when  employed  as  a  green  manure,  was  made  apparent  by  the  pre- 
liminary studies  made  in  1917  on  the  University  North  Farm,  at 
Urbana.  Consequently  extended  investigations  were  conducted  dur- 
ing the  season  of  1919  on  certain  of  the  outlying  experiment  fields  in 
addition  to  continuing  those  already  initiated  at  Urbana. 

CHARACTERISTICS  THAT  MAKE  SWEET  CLOVER  A 
VALUABLE    GREEN-MANURE    CROP 

Sweet  clover  possesses  certain  distinct  characteristics  which  give  it 
a  marked  superiority  over  other  crops  as  a  green  manure  for  nitrate 
production.  The  most  important  of  these  characteristics  are  the  fol- 
lowing : 

1.  Adaptability  to  a  wide  variation  of  climatic  and  soil  condi- 
tions, provided  the  soil  is  not  acid  and  inoculation  is  assured. 

2.  Hardiness  to  cold  and  drouth,  and  resistance  to  diseases  and 
weeds. 

3.  Production  of  a  large  tonnage  per  acre  at  a  time  when  it  can 
best  be  utilized  for  soil  enrichment;   for  example,  its  rapid 
growth  in  the  spring  of  the  second  year  and  during  the  first 
year. 

255 


256  BULLETIN  No.  233  [May, 

4.  Rapid  decomposition  in  the  green  condition. 

5.  Its  deep-rooting  habit  which  enables  it  to  assist  in  rendering 
impervious  subsoils  more  porous  and  to  feed  at  great  depths. 

6.  Ability  to  obtain  plant  food  from  insoluble  minerals  more 
readily  than  other  crops. 

A  crop  that  possesses  the  combined  ability  to  grow  rapidly  in  early 
spring  and  to  decompose  rapidly,  makes  an  ideal  green  manure  for 
feeding  such  a  crop  as  corn.  By  virtue  of  its  rapid  rate  of  growth  and 
large  dry-matter  production,  it  conserves  large  amounts  of  soluble 
plant  food,  especially  at  times  when  the  soil  would  otherwise  suffer 
heavy  losses.  It  possesses  in  common  with  other  legumes,  when  prop- 
erly inoculated,  the  property  of  utilizing  atmospheric  nitrogen.  This 
plant  stores  in  its  roots  large  amounts  of  reserve  food  (especially 
nitrogen),  which  becomes  available  upon  growth  in  the  spring  of  the 
second  year.  The  leaves  are  very  tender  and  decay  rapidly  when  the 
crop  is  turned  under  green.  The  roots  and  stems  decompose  at  slower 
rates  than  the  tops.  Thus  the  three  different  parts  represent  three 
sources  of  nitrogen  that  furnish  three  rates  of  nitrate  production. 

Once  a  weed  by  law,  sweet  clover  is  now  coming  to  be  regarded  by 
soil  scientists  as  the  greatest  crop  for  soil  improvement.  Few  soils  are 
able  to  meet  large  crop  demands  for  nitrate  nitrogen.  Since  sweet 
clover  will  supply  nitrogen  at  an  insignificant  cost,  it  could  well  be 
utilized  as  a  green  manure  by  most  farmers.  Wide  use  of  it  for  soil 
improvement  is  sure  to  be  made  in  many  countries. 

STUDIES  BY  OTHER  INVESTIGATORS  ON  SWEET  CLOVER 
AS  A  GREEN  MANURE 

The  literature  concerning  sweet  clover  as  a  green  manure  and  as  a 
nitrate  producer  is  indeed  very  meager.  Having  long  been  classed  as 
a  weed,  it  has  received  but  very  little  consideration  by  agricultural 
investigators. 

Orth,  in  1890,  was  the  first  scientist  to  test  green  sweet  clover  in 
comparison  with  manure.  Eight  tons  of  stable  manure  were  found  to 
be  decidedly  inferior  to  green  sweet  clover  for  the  production  of  pota- 
toes in  his  experiment.  The  green  sweet  clover  also  gave  large  in- 
creases over  no  treatment  in  the  yields  of  oats  and  corn. 

The  late  Doctor  C.  G.  Hopkins  early  recognized  the  promise  offered 
by  sweet  clover  as  a  green  manure.  In  his  book  on  ' '  Soil  Fertility  and 
Permanent  Agriculture ' '  he  says  of  it : 

— but  it  does  give  promise  of  great  value  as  a  green-manure  crop, 
and  it  seems  appropriate  to  emphasize  the  fact  that  6.4  tons  of  dry 
matter  furnish  as  much  humus-forming  material  and  as  much  nitrogen 
as  would  be  furnished  by  25  tons  of  average  farm  manure." 


SWEET  CLOVER  FOB  NITRATE  PRODUCTION  257 

The  reader  is  requested  to  view  the  results  herein  reported  in  the  light 
of  the  prediction  made  by  our  former  colleague.  So  firm  was  the 
belief  of  Doctor  Hopkins  in  the  importance  of  sweet  clover  that  he 
introduced  it  into  the  rotations  on  most  of  the  forty  experiment  fields 
thruout  the  state.  It  is  interesting  to  note  that  he  selected  sweet 
clover  as  the  crop  upon  which  to  base  his  foundation  work  for  restoring 
the  soils  of  Greece. 

Maynard,  in  1917,  studied  the  decomposition  of  sweet  clover  for 
nitrate  production  under  greenhouse  conditions  and  found  it  to  be 
very  rapid.  The  following  quotation  from  his  review  of  the  literature 
is  of  interest  in  connection  with  the  studies  reported  herein:  "No 
record  has  been  found  of  any  study  of  the  rate  of  decay  of  sweet 
clover  as  a  green  manure." 

The  work  of  Mertz  deserves  special  consideration  as  it  represents 
an  experiment  especially  designed  to  study  the  value  of  green  manures, 
both  legumes  and  non-legumes,  the  latter  being  reinforced  with  com- 
mercial nitrogen.  The  experiment  was  conducted  in  southern  'Cali- 
fornia. The  green  manures  were  grown  in  the  winter  and  were  fol- 
lowed by  corn,  potatoes,  cabbage,  beets,  sorghum,  and  Sudan  hay  dur- 
ing the  six  years  of  the  experiment.  The  legumes  proved  much 
superior  to  the  non-legumes  as  green  manures.  Of  the  legumes,  bitter 
clover  (Melilotus  indica},  an  annual  variety  of  sweet  clover,  was  the 
most  promising,  both  from  the  standpoint  of  vigor  and  of  available 
supplies  of  seed.  Its  value  as  a  green  manure  is  brought  out  in  the 
following  statements  by  Mertz  in  Bulletin  292  of  the  California  Ex- 
periment Station:  "The  use  of  Melilotus  indica  as  a  green-manure 
crop  resulted  in  a  gain  over  adjacent  non-legume  plots  of  nearly  twenty 
bushels  of  shelled  corn  per  acre.  This  is  certainly  indicative  of  the 
manurial  value  of  this  plant."  Another  statement  which  serves  well 
as  a  direct  answer  to  those  who  desire  data  on  comparative  tests  of 
commercial  nitrogen  and  "home-grown"  nitrogen  is  as  follows:  "It 
is  significant  that  the  non-legume  plot  receiving  nitrogen  at  the  rate 
of  163  pounds  per  acre,  gave  for  the  six  years  an  average  increase  of 
51  percent,  while  the  plot  where  Melilotus  indica  was  used  as  a  green 
manure  showed  an  increase  of  57  percent  without  the  addition  of  any 
nitrogenous  fertilizer. ' ' 

The  forms  of  nitrogen  used  in  the  above  experiment  were  sodium 
nitrate  during  the  years  1910-1913,  and  dried  blood  during  1914-1915. 
The  annual  application  of  the  sodium  nitrate  was  1,080  pounds  per 
acre  and  of  the  dried  blood,  1,200  pounds.  The  annual  expense  of 
the  nitrogen  in  the  sodium  nitrate  was  from  $30  to  $35  per  acre. 

In  addition,  it  might  be  said  that  the  legume  plots  had  gained  400 
pounds  of  total  nitrogen  per  acre  over  the  non-legume  plots,  to  a  depth 
of  two  feet,  according  to  the  analysis  reported.  No  nitrate  determina- 
tions were  reported  in  this  work. 


258  BULLETIN  No.  233 

PLAN  OF  INVESTIGATION 

The  investigation  reported  herein  consisted  of  a  study  of  the  nitrate 
content  of  the  surface  soil,  during  the  important  periods  of  the  season, 
of  plots  where  sweet  clover  was  used,  where  stable  manure  was  applied, 
and  where  there  was  no  treatment.  The  sweet-clover  and  manure 
plots  receive  limestone  at  the  rate  of  two  tons,  and  phosphorus  at  the 
rate  of  one  ton,  per  acre,  once  in  four  years.  One  untreated  plot  at 
each  end  of  the  series  was  selected  for  a  study  of  the  nitrate  content 
of  the  natural  soil  subjected  to  crop  rotation  only.  The  plots  which 
are  designated  as  sweet-clover  plots  receive  wheat  straw  in  accordance 
with  the  practice  of  returning  to  the  soil  the  crop  residues  in  the  grain 
system  of  farming.  It  is  found  in  actual  practice,  however,  that 
manure  carries  large  amounts  of  straw,  perhaps  as  much  as  is  applied 
in  the  grain  system  of  farming.  Since  straw  is  recognized  as  a  rela- 
tively unimportant  factor  in  nitrate  production,  this  variation  in  the 
treatment  of  the  plots  does  not  interfere  with  their  value  as  a  basis 
for  comparing  the  two  sources  of  nitrogen. 

In  order  that  the  study  might  include  the  conditions  and  soils  of 
northern,  central,  and  southern  Illinois,  representative  fields  in  these 
sections  of  the  state  were  selected  for  study.  These  fields  are  located 
at  Urbana,  in  Champaign  county;  at  Minonk,  in  Woodford  county; 
at  Oblong,  in  Crawford  county;  at  Toledo,  in  Cumberland  county; 
and  at  Newton,  in  Jasper  county.  The  soil  of  the  first  two  is  a  brown 
silt  loam,  the 'common  soil  of  the  corn  belt,  and  that  of  the  last  three 
is  gray  silt  loam.  Samples  of  soil  were  collected  as  described  in  Bulle- 
tin 225  of  this  station  and  analyzed  by  a  recognized  method. 

Corn  occupied  all  the  plots  from  which  these  results  are  reported. 
No  better  crop  could  have  been  selected  to  have  growing  on  the  soil 
for  the  purpose  of  this  study  than  corn  because  of  its  large  demand  for 
nitrate  nitrogen  during  a  limited  period  of  time.  This  demand  most 
frequently  occurs  from  June  25  to  July  15.  If  the  nitrogen  is  present, 
a  very  large  percentage  of  the  amount  required  to  produce  the  crop 
will  be  taken  up  in  a  few  days.  Thus  it  will  be  seen  that  these  investi- 
gations were  conducted  under  conditions  typical  of  those  that  will  be 
met  in  a  practical  solution  of  the  nitrate  problem. 

In  most  cases,  the  dry  and  the  green  weights  of  the  sweet  clover 
and  the  field  weights  of  the  manure  are  reported.  The  analyses 
of  the  clover  tops  are  also  reported.  In  considering  the  comparisons 
between  the  sweet-clover  plots  and  the  manure  plots,  it  should  be 
borne  in  mind  that  the  manure  used  varies  considerably  in  quality, 
and  that  it  is  not  applied  under  ideal  conditions  to  conserve  its  greatest 
value. 


SWEET  CLOVER  FOR  NITRATE  PRODUCTION  259 

SWEET  CLOVER  FOR  NITRATE  PRODUCTION  ON 
BROWN  SILT  LOAM 

The  layman  often  thinks  of  brown  silt  loam  as  black,  rich,  corn- 
belt  soil,  that  has  no  need  for  additional  organic  matter  or  for  increased 
nitrate  production.  This  is  not  a  safe  assumption,  as  much  of  the  best 
corn-belt  soil  responds  readily  to  additions  of  active  organic  matter. 
The  total  nitrogen  content  of  a  soil  has  been  erroneously  regarded 
as  indicative  of  its  ability  to  supply  nitrate  nitrogen  to  crops.  If  one 
soil  has  5,000  pounds  of  nitrogen  in  the  surface  6%  inches  and  another 
has  2,000  pounds,  there  has  been  little  discussion  as  to  which  would 
supply  the  most  nitrate  to  a  growing  crop.  The  total  nitrogen  is  not, 
however,  a  criterion  as  to  the  availability  of  the  nitrogen  if  the  nitrogen 
happens  to  be  in  a  form  that  is  resistant  to  decay.  Many  peat  soils  are 
poor  nitrate  producers,  yet  they  contain  as  high  as  30,000  pounds 
of  nitrogen  per  acre.  A  small  amount  of  active  nitrogen  in  a  poor 
soil  may  produce  larger  crop  yields  than  a  much  larger  amount  of 
inactive  nitrogen  in  a  rich  soil.  It  is  most  important  to  keep  as  much 
nitrogen  as  possible  in  the  active  state  of  decomposition  at  the  time 
when  it  is  needed  by  crops.  If  this  is  accomplished  by  inoculated 
legumes,  then  the  total  nitrogen  will  at  the  same  time  be  taken  care  of. 

RESULTS  OBTAINED  AT  URBANA,  UNIVERSITY  NORTH  FARM,  1918 

-The  results  of  the  first  special  study  in  which  sweet  clover  was 
plowed  under  as  a  green  manure  are  presented  in  Table  1.  This  work 
was  conducted  at  Urbana  on  Series  300  of  the  University  North  Farm, 
in  1918. 

TABLE  1. — NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1918:    SERIES  300, 
UNIVERSITY  NORTH  FARM,  URBANA 

Pounds  per  acre  in  2  million  pounds  of  surface  soil   (about  0  to  6^  inches),  water-free  basis 


Plot 

Treatment 

Nitrate  nitrogen  in  soil  on 
date  .of  sampling 

Apparent 
utilization 
of  nitrogen 
in  7  days, 
June  24  to 
July 
2 

June 
10 

June 
17 

June 
24 

July 
2 

July 
12 

Aug. 
2 

301 
302 
303 
304 
305 
306 
307 
308 
309 
310 

None  

Ibs. 
22.9 
22.7 
26.6 
62.0 
28.9 
63.6 
19.0 
55.8 
28.8 
90.7 

Ibs. 
34.8 
52.6 
32.6 
66.3 
33.0 
97.0 
34.4 
63.5 
29.4 
96.6 

Ibs. 
30.2 
47.8 
38.0 
48.9 
33.0 
61.5 
33.9 
49.1 
43.6 
81.5 

/6s. 
28.2 
26.0 
22.2 
16.8 
15.9 
21.4 
23.0 
21.5 
27.2 
42.9 

Ibs. 
30.3 
40.0 
29.9 
20.7 
15.6 
16.0 
23.5 
16.5 
20.4 
30.2 

Ibs. 
26.8 
29.3 
21.1 
19.3 
27.9 
22.7 
22.0 
20.0 
16.2 
20.8 

Ibs. 
2.0 
21.8 
15.8 
32.1 
17.1 
40.1 
10.9 
27.6 
16.4 
38.6 

R,SwCl  

M  

RL,  Sw  Cl  

ML  

RLP,SwCl  

MLP  

RLPK,  Sw  Cl.  . 

MLPK  

MxLPx  

R= Residues 

Sw  Cl  =  Sweet  clover  green  manure 

M= Manure 


L= Limestone 

P  — Rock  phosphate  or  bone  meal 

K— Potassium 

X=5  times  usual  application 


260  BULLETIN  No.  233  [May, 

The  figures  given  represent  pounds  of  nitrate  nitrogen  per  acre 
in  the  surface  6%  inches.  In  the  last  column  are  shown  the  apparent 
amounts  of  nitrogen  that  were  utilized  by  the  corn  crop  in  seven  days. 
These  are  introduced  to  emphasize  the  fact  that  large  demands  are 
made  upon  the  soil  nitrate  by  the  corn  crop.  These  figures  make  no 
allowance  for  the  nitrate  that  may  have  been  produced  by  the  soil  dur- 
ing this  period  and  assimilated  by  the  crop.  They  may  be  considered  as 
representative  of  the  minimum  amounts  taken  up  by  the  crop,  since 
the  rainfall  was  not  sufficient  to  reduce  the  nitrate  content,  and  the 
utilization  of  nitrate  by  the  bacterial  activities  is  rapidly  decreasing 
at  this  time  of  the  year  in  normal  Illinois  seasons. 

No  dry-matter  nor  nitrogen  determinations  of  the  sweet  clover  were 
made  the  first  year  of  this  study.  The  manure  was  applied  on  January 
7  and  8,  1918,  in  the  following  amounts,  and  remained  on  the  surface 
until  it  and  the  sweet  clover  were  plowed  under  on  May  15. 

Tons  of  manure 

applied, 
field  weight 

Plot  303  13.41 

Plot  305 15.32 

Plot  307  18.10 

Plot  309 18.12 

Plot  310 80.00 

While  it  may  be  convenient  farm  practice  to  apply  manure  in  this 
way,  it  must  be  admitted  that  it  is  poor  economy  because  of  the 
losses  of  plant  food  from  leaching.  An  idea  of  the  serious  losses  that 
may  result  are  given  on  page  44  of  Bulletin  225.  The  point  is  clear, 
however,  that  under  the  systems  practiced,  green  sweet  clover  was 
decidedly  superior  to  farm  manure  for  nitrate  production,  even  when 
the  applications  of  manure  were  as  high  as  eighteen  tons.  Plots  306 
and  307  are  comparable  except  for  the  fact  that  307  has  received 
large  applications  of  manure  for  a  number  of  years  while  sweet  clover 
was  on  this  series  for  the  first  time  this  year.  Since  no  such  increases 
in  nitrate  production  as  are  recorded  here  are  obtained  from  phos- 
phorus or  limestone  applications  on  this  soil,  the  large  increases  must 
be  attributed  to  the  green  sweet  clover. 

The  results  obtained  in  1919  on  Plots  406,  407,  408,  and  409  of 
the  Davenport  series  on  the  University  North  Farm  at  Urbana  are 
presented  in  Table  2. 

It  is  interesting  to  note  that  altho  the  stands  of  sweet  clover  on 
Plots  406  and  408  were  not  high  when  they  were  plowed  under  for  corn 
on  May  2  (see  Table  7),  noticeable  increases  in  nitrate  had  neverthe- 
less occurred  by  May  26.  The  manure  was  applied  January  3,  1919, 
and  the  land  was  plowed  for  corn  on  May  2.  The  weights  of  manure 
reported  are  for  manure  of  ordinary  quality  and  condition  as  hauled 
out  from  a  city  stable  and  weighed  as  applied  to  the  soil. 


1921] 


SWEET  CLOVER  FOB  NITRATE  PRODUCTION 


261 


TABLE  2. — NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1919:     SERIES  400, 
UNIVERSITY  NORTH  FARM,  URBANA 

Pounds  per  acre  in  2  million  pounds  of  surface  soil   (about  0  to  62/>  inches),  water-free  basis 


Field 

Weight  of 
sweet  clover 
(tops  only) 

Nitrate  nitrogen  in  soil  on 
date  of  sampling 

weight 

April 

Plot 

Treatment 

of 
man- 
ure 

Green 

Water- 
free 

26 
(before 

May 
26 

June 

7 

June 
12 

June 
27 

July 
3 

July 
10 

July 
18 

plow- 

ing) 

tons 

tons 

tons 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

406 

RLP,  Sw  Cl 

5  85 

1  06 

9  6 

25  5 

16.4 

23.0 

39.5 

24.2 

29.2 

12.5 

407 

MLP.  

19.79 

25.0 

14.6 

15.5 

28.9 

30.2 

8.3 

13.5 

10.7 

408 

RLPK,SwCl 

6  82 

1  14 

26  4 

48  5 

11  5 

46  1 

66  9 

26  4 

30.9 

15.9 

409 

MLPK  .... 

19.81 

23.0 

12.5 

21.8 

20.7 

28.4 

12.7 

16.2 

11.5 

When  the  land  was  plowed,  striking  differences  were  seen  in  the 
moisture  content  of  the  sweet-clover  plots  and  the  adjacent  manure 
plots.  The  sweet  clover  had  reduced  the  moisture  on  Plot  408,  28  tons 
per  acre,  as  shown  by  a  comparison  of  that  plot  and  Plot  409,  where 
manure  had  been  applied.  The  lower  moisture  content  is  usually  an 
advantage  in  this  climate  at  this  time  of  year,  because  of  the  possi- 
bility it  offers  for  earlier  plowing.  If  the  soil  were  dry  it  would  be 
wise  to  plow  under  the  green  sweet  clover  earlier  in  order  not  to  rob 
the  soil  of  undue  amounts  of  moisture.  The  heavy  rainfall  occurring 
between  May  26  and  June  7  accounts  for  the  low  nitrate  content 
found  on  June  7  (Table  2). 

The  water-free  weights  of  the  sweet  clover  include  only  the  spring 
growth  of  tops.  The  roots,  the  fall  growth,  and  the  residues  left  on 
the  ground  from  the  fall  growth  are  not  reported.  The  nitrogen  con- 
tent of  the  spring  growth  and  other  data  on  sweet-clover  yields  will 
be  found  in  Table  7. 

It  is  interesting  to  note  the  sudden  drop  in  the  nitrate  figures, 
which  is  always  coincident  with  the  rapid  growth  of  the  corn  crop. 
This  year  it  occurred  between  June  27  and  July  3. 

From  this  year's  results  on  the  brown  silt  loam  it  is  evident  that 
nitrate  production  on  this  type  of  soil  is  greatly  enhanced  by  the 
plowing  under  of  green  sweet  clover.  Another  important  fact  is  that 
approximately  one  ton  (water-free  basis)  of  spring  growth  of  sweet- 
clover  tops,  together  with  the  roots  and  fall  residues,  furnished  as 
much  nitrate  as  19.8  tons  of  average  farm  manure. 

RESULTS  OBTAINED  AT  MINONK  FIELD  IN  1919 

The  results  reported  in  Table  3  were  obtained  at  the  Minonk  field, 
in  Woodford  county  in  1919.  The  soil  on  this  field  is  somewhat  uneven, 
being  practically  a  heavy  clay  on  Plots  101  to  106  and  a  brown  silt 
loam  on  Plots  107  to  110. 


262 


BULLETIN  No.  233 


[May, 


The  manure  had  been  applied  on  September  13,  1918.  On  April 
30,  1919,  an  excellent  stand  of  sweet  clover  on  Plot  108  and  the  manure 
on  Plot  104  were  plowed  under.  The  first  samples  of  soil  were  taken 
April  26.  The  relatively  high  nitrate  content  of  Plot  108  is  of  sig- 
nificance. Either  the  protection  afforded  the  soil  by  the  presence  of 
the  fall  and  spring  growths  of  the  sweet  clover,  or  the  decomposition  of 

TABLE  3. — NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1919:     MINONK  FIELD 

Pounds  per  acre  in  2  million  pounds  of  surface  soil   (about  0  to  6%  inches),  water-free  basis 


Plot 

Treatment 

Field 
weight 
of 
manure 

Weight  of 
sweet  clover 
(tops  only) 

Nitrate  nitrogen  in  soil  on 
date  of  sampling 

Green 

Water- 
free 

Apr.  26 
(before 
plowing) 

May 
30 

July 

1 

July 
14 

Aug. 
12 

104 
105 
108 
110 

Manure,  LP 
None  

tons 
20.89 

tons 

tons 

Ibs. 
21.0 
24.5 
38.7 
10.1 

Ibs. 
15.4 
9.3 
76.8 
8.1 

Ibs. 
7.9 
10.8 
67.2 
11.8 

Ibs. 
7.5 
14.5 
51.3 
18.6 

Ibs. 
7.6 
12.4 
143.6 
11.8 

SwCl,LP  . 
None  

9.17 

1.54 

the  fall  growth,  accounts  for  the  38.7  pounds  of  nitrate  nitrogen  found 
before  plowing.  By  comparing  the  manure  plot  and  the  sweet-clover 
plot,  it  will  be  seen  that  the  manure  was  greatly  inferior  to  the  sweet 
clover  for  nitrate  production.  It  was  only  a  little  better  than  were  the 
check  plots,  which  from  all  appearances  were  suffering  from  nitrogen 
starvation  during  the  critical  period  of  crop  growth.  The  amount  of 
manure  applied  was  20.89  tons  per  acre.  The  water-free  weight  of  the 
spring  growth  of  sweet  clover  tops  plowed  under  was  1.54  tons. 

The  large  nitrate  production  in  August  on  the  sweet-clover  plot 
is  worthy  of  note  and  suggests  the  advisability  of  plowing  under  the 
sweet  clover  at  an  earlier  date,  which  would  be  of  advantage  in  effect- 
ing a  somewhat  earlier  decomposition  and  thereby  avoiding  the  detri- 
mental effect  of  the  first  stages  of  decomposition  upon  the  germinating 
crop,  in  conserving  soil  moisture,  and  frequently  in  promoting  farm 
work  in  the  rush  season  of  spring.  Another  suggestion  would  be  the 
utilization  of  the  surplus  nitrate  by  seeding  a  catch  crop,  such  as  rye 
or  wheat,  in  the  corn.  This  shows  what  is  possible  in  the  way  of 
nitrate  production  where  a  large  fall  growth  is  allowed  to  remain  on 
the  soil  and,  together  with  the  spring  growth,  is  plowed  under  for 
corn.  There  was  185.5  pounds  of  nitrogen  turned  under  in  the  spring 
and  fall  tops  alone,  in  addition  to  the  38.7  pounds  of  nitrate  nitrogen 
present  in  the  soil. 

The  value  of  green  sweet  clover  on  this  field  is  apparent  and  needs 
no  further  explanation. 


SWEET  CLOVER  FOR  NITRATE  PRODUCTION 


263 


SWEET   CLOVER  FOR  NITRATE   PRODUCTION  ON 
GRAY  SILT  LOAM  ON  TIGHT  CLAY 

The  need  for  increasing  the  active  organic-matter  content  of  the 
gray  silt  loam  on  tight  clay  is  very  apparent  and  quite  generally 
recognized.  However,  the  very  low  nitrate  efficiency  of  this  type  of 
soil  is  not  so  well  understood. 

RESULTS  OBTAINED  AT  TOLEDO  FIELD  IN  1919 

The  Toledo  field  is  located  in  Cumberland  county  on  the  soil  type 
designated  as  gray  silt  loam  on  tight  clay.  The  manure  was  applied 
in  the  fall  of  1918  and  the  sweet  clover  and  the  manure  were  plowed 
under  on  May  13,  1919.  Corn  was  planted  on  May  30.  The  applica- 
tion of  manure  was  6.25  tons,  while  the  water-free  weight  of  green 
sweet  clover  of  spring  growth  was  2.43  tons.  The  sweet  clover  grew 
taller  than  was  desired  because  rains  prevented  earlier  plowing.  From 
Table  7,  it  will  be  seen  that  this  was  the  tallest  crop  that  was  sampled 
on  the  nine  fields  studied.  The  nitrate  results  are  given  in  Table  4. 

TABLE  4. — NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1919:     TOLEDO  FIELD 

Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6?^  inches),  water-free  basis 


Plot 

Treatment 

Field 
weight 
of 
manure 

Weight  of 
sweet  clover 
(tops  only) 

Nitrate  nitrogen  in  soil  on 
date  of  sampling 

Green 

Water- 
free 

May  12 

(before 
plowing) 

June 
18 

July 
4 

July 
17 

Aug. 
18 

104 
105 
108 
110 

Manure  ,LP 
None  

tons 
6.25 

tons 

tons 

Ibs. 
13.0 
6.0 
7.0 
8.1 

Ibs. 
15.5 
13.6 
31.5 
8.0 

Ibs. 
11.8 
12.1 
30.3 
7.3 

Ibs. 
11.7 
9.1 
15.9 
8.9 

Ibs. 
19.0 
27.0 
34.2 
24.1 

Sw  Cl,  LP  . 
None  

12.87 

2.43 

Nitrate  production  on  the  sweet-clover  plot  was  considerably 
superior  to  that  on  the  manure  plot.  The  nitrate  content  of  the  check 
plots  increased  from  July  17  to  August  18,  and  it  should  be  said  that 
on  these  plots  there  was  practically  no  crop  to  use  the  nitrate.  The 
accumulation  of  nitrate  on  the  checks  between  May  12  and  August  18 
was  16  and  21  pounds.  The  manure  plot  supported  a  good  crop  and 
increased  6  pounds,  while  the  sweet-clover  plot  supported  a  good  crop 
and  increased  27  pounds. 

The  sweet  clover,  even  in  the  dry  months  of  July  and  August,  has 
demonstrated  that  its  decomposition  will  supply  nitrate  in  ample 
quantities  for  the  corn  crop  on  one  of  the  poorest  types  of  soil 
recognized. 


264 


BULLETIN  No.  233 
RESULTS  OBTAINED  AT  NEWTON  FIELD  IN  1919 


[May, 


At  Newton  the  difficulties  encountered  were  greater  than  at  Toledo, 
and  yet  the  value  of  sweet  clover  on  this  exceptionally  poor  soil  was  out- 
standing, as  may  be  seen  by  reference  to  Table  5. 

The  plowing  under  of  the  manure  and  sweet  clover  was  delayed  by 
rain,  and  planting  was  not  possible  until  very  late.  But  2.18  tons  of 
manure  was  applied,  and  it  was  put  on  in  the  winter.  The  water-free 
weight  of  green  sweet  clover  of  spring  growth  was  2.29  tons  on  May 
10,  but  the  land  was  not  plowed  until  the  first  week  in  June,  and  the 
corn  was  planted  June  13.  The  sweet  clover  was  22  inches  high  on 
May  10,  and  much  taller  on  June  1.  This  more  advanced  development 
undoubtedly  greatly  reduced  the  immediate  yields  of  nitrate. 

On  the  two  check  plots  the  amounts  of  nitrogen  reported  as  pres- 
ent on  August  18  represent  nearly  the  total  seasonal  production,  for 
only  a  very  small  amount  was  used  by  the  crop.  The  amount  of  manure 
applied  to  the  manure  plot  was  too  small  to  permit  of  a  legitimate 
comparison  of-  that  plot  with  the  sweet-clover  plot,  but  both  these 
treated  plots  supported  larger  crops  than  the  checks,  and  the  sweet- 
clover  plot  at  the  same  time  accumulated  striking  amounts  of  nitrate 
nitrogen. 

TABLE  5. — NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1919:     NEWTON  FIELD 
Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6%  inches),  water-free  basis 


Plot 

404 
405 
408 
410 

Treatment 

Field 
weight 
of 
manure 

Weight  of 
sweet  clover 
(tops  only) 

Nitrate  nitrogen  in  soil  on 
date  of  sampling 

Green 

Water- 
free 

May  12 

(before 
plowing) 

June 
18 

July 
4 

July 
17 

Aug. 
18 

Manure,  LP 
None  

tons 
2.18 

tons 

tons 

Ibs. 
13.2 
4.7 
18.6 
14.0 

Ibs. 
17  A 
18.3 
36.8 
22.6 

Ibs. 
7.0 
6.6 
30.6 
9.2 

Ibs. 
11.7 
8.9 
13.9 
9.7 

/6s. 
16.0 
21.7 
78.2 
25.9 

Sw  Cl,  LP 
None  

12.6 

2.29 

RESULTS  OBTAINED  AT  OBLONG  FIELD  IN  1919 

The  Oblong  field  represents  better  soil  than  that  found  at  Newton 
or  Toledo. 

The  weight  of  manure  applied  was  6.42  tons  per  acre,  and  the  ap- 
plication was  made  late  in  the  fall.  The  land  was  plowed  May  17  and 
the  corn  planted  May  31.  Altho  no  sweet-clover  samples  were  obtained 
from  this  field,  it  is  believed  that  as  much  sweet  clover  was  plowed 
under  as  at  Newton.  The  crop  of  corn  developed  normally  on  the 
manure  and  the  sweet-clover  plots.  On  June  18  the  manure  plot  was 
the  highest  in  nitrate  content,  and  apparently  met  the  demands  of  the 


SWEET  CLOVER  FOB  NITRATE  PRODUCTION 


265 


crop  satisfactorily.  The  nitrate  produced  from  the  sweet  clover  was 
ample,  but  was  undoubtedly  less  than  it  would  have  been  if  the  clover 
had  been  plowed  under  before  it  had  become  woody.  Apparently  little 
loss  occurred  in  the  manure  applied  on  this  field  this  year. 

The  figures  in  Table  6  indicate  the  same  condition  of  decomposition 
as  that  found  on  the  Toledo  and  Newton  fields.  Earlier  plowing  would 
have  furnished  more  nitrate  and  at  an  earlier  period.  Delayed  plowing 
gives  the  plant  time  to  render  its  nitrogen  compounds  more  stable,  and 
this  slows  down  the  rate  of  nitrate  production,  but  the  disadvantage  in 
the  slower  nitrate  production  which  results  from  allowing  the  clover 
to  become  more  mature  is  in  part  offset  by  the  greater  amount  of  total 
nitrogen  which  the  more  mature  clover  contains  and  which  will  ulti- 
mately become  available  for  plant  use  in  the  form  of  nitrate  nitrogen. 

Because  of  losses  which  frequently  occur  one  must  calculate  on  a 
nitrate  accumulation  that  will  somewhat  more  than  meet  crop  needs. 
Since  the  greatest  losses  of  nitrogen  from  the  soil  generally  occur 
in  the  spring,  it  is  of  particular  advantage  to  have  the  nitrogen  at 
this  time  of  year  in  a  form  which  will  not  leach  readily.  This  means 
that  it  should  be  either  in  active  organic  form  or  in  a  growing  crop.  In 
the  plowing  under  of  sweet  clover,  little  of  the  nitrogen  so  added  to  the 
soil  is  lost  by  leaching,  even  after  plowing  if  it  is  done  about  May  1, 

TABLE  6. — NITRATE  NITROGEN  IN  SOIL  GROWING  CCRN  IN  1919:    OBLONG  FIELD 

Pounds  per  acre  in  2  million  pounds  of  surface  soil   (about  0  to  6J3  inches),  water-free  basis 


Plot 

104 
105 
108 
110 

Treatment 

Nitrate  nitrogen  in  soil  on  date  of  sampling 

June  18 

July  4 

July  17 

August  18 

Manure,  LP  

Ibs. 
53.2 
16.8 
39.1 
11.2 

Ibs. 
22.1 
27.6 
19.2 
16.1 

Ibs. 
20.0 
14.2 
16.3 
15.7 

Ibs. 
21.0 
27.5 
58.1 
29:0 

None  

Sweet  clover,  LP   .  .  . 

None  . 

since  the  process  of  nitrification  will  not  ordinarily  produce  large 
amounts  of  nitrate  before  21  to  28  days  have  elapsed.  As  earlier  stated, 
this  first  rapid  production  is  mostly  from  the  leaves.  Later  the  stems 
and  roots  produce  nitrate.  They  act  as  a  reserve  supply,  or  as  a  second 
application  of  nitrate,  and  on  account  of  their  composition  are  likely 
to  suffer  little  loss  from  leaching,  while  the  nitrogen  of  nitrate  of  soda, 
ammonium  sulfate,  and  other  soluble  forms  of  nitrogen  is  readily  lost 
under  similar  conditions. 


266 


BULLETIN  No.  233 


[May, 


WEIGHTS  AND  NITROGEN  CONTENT  OF  SWEET  CLOVER 

In  Table  7  are  found  the  results  of  studies  made  on  samples  of 
sweet-clover  tops  of  spring  growth  of  the  second  year,  cut  from  one 
square  yard.  Every  precaution  was  exercised  to  cause  the  results  to 
represent  the  minimum. 

The  Urbana,  Minonk,  and  Joliet  fields  represent  central  and  north- 
ern Illinois  conditions,  while  the  others  represent  southern  Illinois 
conditions. 

The  stands  on  all  fields  except  at  Urbana  were  excellent.  Plot  406 
at  Urbana  had  the  poorest  stand.  The  earlier  season  in  southern 
Illinois  gives  the  sweet  clover  an  opportunity  to  grow  to  a  greater 
height  in  the  same  time  than  in  central  or  northern  Illinois.  The 
southern  fields  would  have  been  plowed  earlier  if  rain  had  not  inter- 
fered. 

The  weights  of  material  produced  were  much  greater  on  the  south- 
ern fields  than  on  the  central  and  northern  fields,  altho  the  percentages 
of  nitrogen  ran  consistently  lower.  This  is  accounted  for  by  the 
heavier,  more  woody  growth,  as  indicated  by  the  height.  The  smaller 
weights  of  material  on  the  central  and  northern  fields,  as  compared 
with  those  of  the  southern  fields,  are  partially  offset  by  the  richer  crop 
growth. 

The  most  important  consideration  is  the  weight  of  nitrogen  in  the 
crop  on  the  acre  basis.  As  shown  in  Table  7,  the  amount  of  nitrogen 
in  the  tops  at  sampling  time  varied  from  98  to  196  pounds.  The 
sweet-clover  plot  at  Toledo  produced  80.6  pounds  of  available  nitrogen, 
including  the  nitrate  nitrogen  found  on  August  18  and  the  amount 
taken  from  the  soil  by  a  crop  of  30.9  bushels  of  corn.  At  the  time  the 


TABLE  7.  — WEIGHTS  AND  NITROGEN  CONTENT  OF  SWEET-CLOVER  TOPS  OF  SPRING 

GROWTH:    1919 

Acre  basis 


Field 

Plot 

Date 
sample 
was 
taken 

Height 

Green 
weight 

Water  content 

Water-free 
material 

Weight 
of 
nitrogen 
per  acre 

Percent- 
age 
of  water 

Weight 
of  water 

Weight 

Percent- 
age of 
nitrogen 

Urbana.  
Urbana  
Urbana  
Minonk  .... 
Joliet  

408 
408 
406 
108 
508 
108 
408 
108 
108 

April  24 
May  2 
May  2 
April  26 
April  29 
May  9 
May  10 
May  1 
May  1 

inches 
10 
14 
13 
12 
9.5 
26 
22 
19 
18 

tons 
5.07 
6.82 
5.85 
9.17 
7.96 
12.87 
12.60 
12.70 
8.71 

perct. 
82.2 
83.5 
81.8 
83.1 
81.9 
81.0 
81.0 
86.1 
82.2 

tons 
4.16 
5.70 
4.78 
7.63 
6.52 
10.38 
9.80 
10.98 
7.65 

tons 
.95 
1.12 
1.06 
1.54 
1.44 
2.43 
2.29 
1.76 
1.66 

perct. 
4.60 
4.50 
4.62 
5.35 
4.60 
4.03 
4.10 
3.67 
4.00 

Ibs. 
83.3 
100.9 
98.1 
164.8 
133.3 
196.4 
188.5 
129.6 
124.8 

Toledo  

Newton  .... 
Raleigh.  .  .  . 
Enfield  

1921}  SWEET  CLOVER  FOE  NITRATE  PRODUCTION  267 

sweet  clover  on  this  same  plot  was  sampled  (May  9),  it  had  accumu- 
lated in  the  tops  of  the  second-spring  growth  196.4  pounds  of  nitrogen, 
or  nearly  two  and  one-half  times  as  much  as  was  produced  in  the  soil 
while  the  corn  crop  was  growing,  even  with  sweet  clover  to  assist  in 
the  production.  Further  the  untreated  soil  produced  only  27  pounds 
of  nitrate  nitrogen  up  to  August  18,  and  limestone  and  phosphorus 
together,  while  increasing  nitrate  production  above  that  of  the  un- 
treated soil,  were  not  able  to  cause  increases  sufficient  to  account  for 
the  large  amount  of  nitrogen  in  the  tops  alone.  This  evidence  indi- 
cates that  a  very  large  fixation  of  nitrogen  by  sweet  clover  takes  place 
on  the  gray  silt  loam  types.  Probably  the  fixation  is  smaller  on  the 
-  brown  silt  loam,  but  even  there  it  is  large  under  favorable  conditions. 

In  considering  the  merits  of  sweet  clover,  its  ability  to  conserve 
nitrate  is  also  a  large  factor  that  should  not  be  overlooked.  In  some 
cases  the  conservation  of  nitrogen  may  be  as  important  as  its  addition. 

Sweet  clover,  when  seeded  in  small  grains  and  allowed  to  grow  until 
time  to  plow  for  corn,  supplies  large  amounts  of  total  nitrogen  to  the 
soil.  It  decomposes  rapidly  and  furnishes  a  sufficient  amount  of 
nitrate  nitrogen  for  a  large  corn  crop.  In  these  studies,  the  tops,  on 
a  water-free  basis,  averaged  4.38  percent  of  nitrogen  for  all  the  fields. 
This  means  87.6  pounds  of  nitrogen  per  ton  of  dry  weight.  That  the 
roots  weigh  as  much  or  more  than  the  tops  at  this  time  of  year,  is 
known,  and  the  nitrogen  content  is  not  much  lower  than  that  of  the 
tops.  This  would  indicate  that  there  is  nearly  twice  as  much  nitrogen 
in  the  entire  plant  as  these  figures  given  for  the  tops  show.  At  the 
Toledo  field,  where  the  sweet  clover  grew  to  a  height  of  26  inches 
before  being  plowed  under,  2.43  tons  of  tops  (water-free  basis)  con- 
tained as  much  nitrogen  as  20  tons  of  average  farm  manure. 

CONCLUSIONS 

1.  Sweet  clover,  when  plowed  under  as  a  green  manure  for  corn, 
furnishes  large  amounts  of  nitrate  nitrogen  for  that  crop.    The  data 
on  which  this  statement  is  based  were  obtained  from  experiment  fields 
in  northern,  central,  and  southern  Illinois,  located  on  brown  silt  loam 
and  on  gray  silt  loam  on  tight  clay. 

2.  The  large  nitrogen  content  of  sweet  clover  indicates  that  a  large 
fixation  of  nitrogen  occurs  on  these  soils.    In  the  present  study  the 
sweet-clover  tops  averaged  87.6  pounds  of  nitrogen  per  ton  of  dry 
matter  at  sampling  time,  which,  in  some  cases,  was  about  the  time  of 
plowing  for  corn  while  in  others  it  was  somewhat  earlier. 

3.  The  data  reported  herein  furnish  positive  information  con- 
cerning the  value  of  sweet  clover,  when  used  as  a  green  manure,  for 
solving  the  problem  of  adding  to,  conserving,  and  making  available  for 
crop  purposes  the  nitrogen  of  the  soil. 


UNIVERSITY  OF  ILLINOIS-URBAN* 


